1. Field of Invention
This invention relates to automatic test systems for digital electronic converters and particularly to methods and apparatus for testing analog-to-digital converters and digital-to-analog converters.
Converters between the digital and analog domains are employed to interface digital electonic circuitry and devices producing analog signals. Accuracy of conversion, gain and repeatability in the process of conversion are characteristics which are important to evaluate, and if possible, characteristics for which an optimized calibration procedure is desireable.
2. Description of the Prior Art
Current state of the art testing techniques for converters are generally limited to testing a few states, such as major transitions for analog-to-digital converters and such as the simple binary weights and full-scale amplitude for digital-to-analog converters. Substantially all tests are static in nature and are incapable of providing a complete statistical evaluation of the converter.
Dynamic testing techniques have been suggested for limited purposes. An example is a method proposed by L. F. Pau and presented in a paper entitled "Fast Testing and Trimming of A/D and D/A Converters in Automatic Test Systems" at the 1978 IEEE Autotest Conference. Pau has suggested one method of dynamic testing employing excitation signals characterized by Walsh functions. The evaluation method presupposes the use of an ideal reference device, the output response of which is employed with the output response of a device under test to generate an error signal from which optimization decisions are made. A device built according to the techniques suggested by Pau is therefore limited by the accuracy of the referenced device.